The present invention relates to hydraulic brake systems and more particularly to a booster mechanism for park brakes of hydraulic brake systems.
Hydraulic brake systems are implemented in a number of vehicles, including automobiles and golf carts. To function, such brake systems rely on fluid pressure within the system to actuate a single brake or multiple brakes. In essence, a master cylinder is selectively actuated by a brake pedal, whereby a brake piston of the master cylinder induces fluid pressure within the brake system, thereby actuating the brakes. Most vehicles include a park brake for continuous engagement of the brakes over an extended period of time. In this manner, a vehicle may be at rest with the brakes prohibiting rolling. Typically, the park brake includes a mechanically actuated brake functioning independently from the hydraulic brake system. However, it is known in the art to incorporate a park brake with the hydraulic brake system. Examples of such a system for a golf cart can be found with reference to U.S. patent application Ser. No. 09/846,031, filed Apr. 30, 2001; U.S. patent application Ser. No. 09/517,302, filed Mar. 2, 2000, now U.S. Pat. No. 6,223,865 B1, which claims the benefit of U.S. Provisional Serial No. 60/122,405, filed Mar. 2, 1999, all of which are assigned to the assignee of the present invention. The disclosures of the above are incorporated by reference.
One fundamental problem with park brake incorporating hydraulic brake systems is that the hydraulic fluid experiences significant density and therefore volume changes as the temperature of the surrounding environment changes. For example, a constant mass of hydraulic fluid expands, becoming less dense and encompassing more volume at a higher temperature and contracts, becoming more dense and encompassing less volume at a lower temperature. Such fluctuations in the hydraulic fluid characteristics may result in reduced fluid pressure within the brake system, causing the park brake to be insufficient for engaging the brakes.
To remedy this situation existing brake systems include an energy accumulator which stores energy that is later used to compensate for such pressure losses. Generally, the accumulator includes a secondary or accumulator piston in fluid communication with the hydraulic brake system and biased by a spring. When the park brake is applied, the accumulator piston compresses the spring a distance, and the fluid pressure within the brake system holding the spring is compressed. As fluid density decreases, such as with a temperature drop over seasonal changes, system pressure losses are compensated for by the spring biasing the accumulator piston, with the accumulator piston maintaining the system pressure. However, as soon as the spring achieves full extension, or bottoms out against a fixed object, it is no longer able to bias the accumulator piston and thus, no longer maintain system pressure.
It is therefore desirable to provide a mechanism for enabling increased spring extension range. In this manner, the accumulator piston is able to maintain system pressure over a longer period of time and within environments of significantly decreasing temperatures.
Accordingly, the present invention provides a brake assembly for implementation with a hydraulic brake system. The brake assembly includes an accumulator piston in fluid communication with the hydraulic brake system to maintain hydraulic pressure therewithin, an accumulator assembly operably engaging the accumulator piston and including a compression plate engaging the accumulator piston and an accumulator spring biasing the compression plate against the accumulator piston, and a booster arm pivotally supported by one of the support bracket and the master cylinder, and actuable between first and second positions, wherein in the first position the booster arm limits axial movement of the compression plate against the accumulator piston and wherein in the second position the booster arm permits increased axial movement of the compression plate against the accumulator piston.
More particularly, the present invention provides a brake assembly for implementation with a hydraulic brake system. The brake assembly includes a support bracket, a master cylinder supported by the support bracket and operable to selectively provide hydraulic pressure to the hydraulic brake system, an accumulator piston extending from the master cylinder and operable to enable function of the master cylinder. The accumulator piston is operable to maintain hydraulic pressure within the hydraulic brake system. An accumulator assembly is included and extends from the support bracket. The accumulator assembly has a compression plate engaging the accumulator piston, an end cap and an accumulator spring disposed between the compression plate and the end cap and biasing the compression plate against the accumulator piston. A booster arm is pivotally supported by one of the support bracket and the master cylinder, and is actuable between first and second positions, wherein in the first position the booster arm limits axial movement of the compression plate against the accumulator piston and wherein in the second position the booster arm permits increased axial movement of the compression plate against the accumulator piston.
In the first position, the booster arm defines a normal xe2x80x9cbottom-outxe2x80x9d position of the compression plate, whereby the compression plate is unable to further act on the accumulator piston due to the biasing force of the accumulator spring. In the second position, the booster arm is rotated away from limiting axial movement of the compression plate, defining a new xe2x80x9cbottom-outxe2x80x9d position of the compression plate, thereby enabling increased distance for the compression plate to act on the accumulator piston.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.